In the medical arts and sciences, it is routinely required to probe internal parts of the body by coupling signals of various signal types to the skin, for transmitting the signals through the skin and into the body, or for receiving signals through the skin for input to a signal measuring or analyzing device. This may be for the purpose of imaging or source localization, or for stimulating internal tissue.
For example, in electroencephalography (“EEG”) and electrocardiography (“ECG”), surface electrodes placed on the skin receive electric signals generated from within the body to probe the electrical output of the brain and heart, respectively. Conversely, electric signals are transmitted through the skin and into the body in electrical impedance tomography (“EIT”), to probe the body in a stimulative sense for the purpose of obtaining images.
An advantage recognized by one of the present inventors and that has been described in U.S. Pat. No. 6,330,470 to Tucker, Ferree and Ericksen, incorporated by reference herein, results from placing a transmitting or stimulating electrode at the same location as a receiving electrode for more efficiently locating electrical sources in the body as well as for more precisely and efficiently imaging the body.
It is also common practice to probe the body in a stimulative sense with acoustic signals, such as in ultra-sound diagnostic imaging (“UI”), and to a lesser extent optical signals, such as in near-infrared spectroscopy and optical tomography (“NIR OT”).
Each of these signal types, i.e., electrical, acoustical, and optical, provides particular advantages and disadvantages for probing the body. Accordingly, in the prior art, one of the signal types has been selected in preference to the others to suit the particular purpose at hand. For example, EIT employs electric signals to probe the electrical characteristics of the body, particularly conductive properties. NIR OT uses near-infrared electromagnetic signals, i.e., light-waves, which propagate with minimal absorption through soft tissue. These are particularly useful to image hard tissue such as bone. On the other hand, acoustic signals are useful for imaging soft tissue.
As explained in the '470 patent, localizing sources of electrical activity within the body by analyzing fields outside the body is computationally difficult, and for the technique to be effective, it is necessary to reduce ambiguities as much as possible. This can be done by increasing the number of electrodes, but this is costly, and where the electrodes must each be placed on the body, time consuming. Improving resolution in imaging processes also has generally required a greater density of sensing hardware and improved control and precision of probe signal application, which pushes the limits of allowable cost and available technology. The conventional practice of selecting one imaging method for a particular imaging circumstance or need has ensured that the cost and technological limitations of the different types of probing are retained.
Accordingly, there is a need for a method and composition for probing the body through the skin that recognizes the advantages of combining imaging methodologies in overcoming the limitations of the individual imaging methodologies.